Blood vesselsfirst make their appearance in several scattered vascular areas that are developed simultaneously between the entodermand the mesodermof the yolk-sac, i. e., outside the body of the embryo. Here a new type of cell, the angioblast or vasoformative cell, is differentiated from the mesoderm.
These cells as they divide form small, dense
syncytialmasses, which soon join with similar masses by means of fine processes to form plexuses.
Angioblasts are one of the two products formed from
hemangioblasts(the other being pluripotential hemopoietic stem cells).
* [http://www.medicine.uiowa.edu/creative/portfolio.asp?recordID=ILLUSTRATION&index=2 Diagram at uiowa.edu]
* [http://www.brown.edu/Courses/BI0032/stemcell/vascu.htm "Development of the vascular system", at brown.edu]
* [http://7e.devbio.com/article.php?ch=15&id=156 Alternative Sources Of Angioblasts]
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